In its simplest form, a seal assembly for a rotary bearing or the like, such as is used for sealing the wheel spindle assembly of a vehicle, includes at least one annular flexible seal member attached to a seal casing, that in turn flexes against the opposed casing to form a sealing interface around the circular line of contact. The seal allows relative rotation between the coaxial, rotating component parts, while maintaining good sealing contact. This seal is primarily to prevent entry of foreign material into the wheel spindle bearing, such as salt, road grime and other debris. The seals of the prior art seal assemblies are primarily formed of a molded elastomer material, such as rubber, but can also be made of less flexible, but lower friction materials, such as polytetrafloroethelene (PTFE).
In the recent prior art, it is common to provide bearing assemblies in the form of a unitized assembly having inner and outer annular casings that support the flexible seal in between. The casings are ring shaped and are formed of stamped metal with sufficient rigidity to be press fit in between the inner and outer coaxial parts supported by the bearing assembly. It is also common in recent seal technology to provide multiple lips on a single seal. Unfortunately, such a double lip seal is rarely twice as effective as a single lip seal because the lips are not functionally independent. This lack of independence of the two sealing components of the seal inherently leads to progressive deterioration over time. For example, vibration in the common hinge of the double lip seal causes accelerated wear on both sealing edges at the two sealing interfaces. Also, corrosion resulting from salt, or other corrosive materials that are commonly encountered in everyday use of a vehicle, can cause accelerated wear of both sealing edges of the double lip seal since typically the edges engage a common land on the opposed casing.
An example of a unitized seal assembly with multiple lips that has had success in use but is subject to the above drawbacks includes the seal assembly shown and described in U.S. Pat. No. 4,597,495, issued Feb. 5, 1985, and owned by the assignee of the present invention. As disclosed in this patent, the single seal is attached to the inner casing and has two lips that engage the inside sealing surface of the outer casing. As such, the lips share a common hinge point and thus are both subject to wear if vibration occurs in the common hinge. Also, in the event the sealing surface of the outer casing starts to corrode, accelerated wear of the sealing edges of the lips is also inevitable. When vibration at the common hinge and corrosion occur together, further accelerated wear of both edges associated with the double lips of this seal occurs, leading evidently to deleterious seal leakage.
Another approach that has had some success in sealing coaxial, rotatable parts, but generally in different, less hostile environments, includes a seal. An example of this type of seal includes U.S. Pat. No. 4,185,838 issued to Danner on Jan. 29, 1980. This patent discloses two separate seals, one attached each to the inner and outer casings of the seal assembly. In this manner, a seal assembly having two, relatively independent seal interfaces and forming a tortuous path in between, is provided. As shown in this patent, a usual prior art approach is to have this type of seal, to be a non-unitized structure with the sealing interfaces formed by elastomer-to-elastomer sliding contact. Even though this seal assembly works well in relatively shielded environments, it still leaves much to be desired in an hostile environment, such as encountered in protecting the bearing assembly of a vehicle wheel spindle assembly.
Especially in the area of wheel spindle technology, a seal assembly can experience rapid, radial vibrations between the inner and outer casings. These vibrations can cause excessive deterioration of the seals along the circular line of contact with the opposing casing. When the seals become worn due to these vibration forces, they inherently lose their ability to flex rapidly enough to maintain the critical continuous sealing contact with the opposing casing. As this occurs, any corrosion along a sealing land of the casing becomes progressive, thus causing more deterioration of the seal edges, and still more loss of sealing contact. Eventually, contamination of the lubricant within this seal assembly can result, thus, of course, resulting in rough bearing operation, along with increased noise and heat.
Thus, the need is identified to provide an improved type seal that is not only characterized by improved seal effectiveness, but also by a longer useful life. Indeed, the present invention discloses such an improvement and a novel solution to the identified problem.